This invention relates to the preparation of poly(propylene terephthalate) ("PPT") and related copolyesters. In a specific aspect, the invention relates to the treatment of a byproduct-containing stream in a PPT preparation process.
The preparation of PPT involves the reaction of terephthalic acid and excess 1,3-propanediol (PDO) at about 250.degree. C. under pressure to form an oligomer and water. The water is then distilled from the PPT. The major by-products of the polymerization reaction, acrolein and allyl alcohol, are contained in solution in the distillate.
Although the amount of these byproducts is low, it would be desirable to further reduce the level of byproducts in the aqueous distillate especially for subsequent activated sludge treatment.
It is therefore an object of the invention to provide a process for preparing a 1,3-propanediol-based polyesters in which the level of acrolein byproduct in the aqueous stream distilled from the product polyester is reduced.